This invention relates to an optical assembly for use in a barcode reader and, in particular, to an optical assembly that is capable of maximizing the light produced by a plurality of light emitting diodes to provide a high intensity image of a barcode target at the image recording surface of a solid state imager.
Although the advantages associated with light emitting diodes (LEDs) when used in barcode scanning equipment are well known, the level of the intensity produced by this type of lamp is relatively low when compared to other light sources such as halogen lamps or arc lamps. In an effort to improve the effectiveness of light emitting diodes in this application, it is sometimes customary to employ a relatively large number of lamps aligned in one or more rows above or below the imaging lens. As a result, the target region, as well as the periphery of the target region, are flooded with an excessive amount of light. This approach, however, is space consuming and poses certain assembly and alignment problems.
Optical units have also been devised for providing coplanar illumination wherein the light emitting diodes are mounted in the same plane as the imaging onto both sides of the imaging lens. The light from the light emitting diodes is further passed through magnifying lens to project the light onto the target region. Additionally, diffusers are used in association with the LEDs to more uniformly distribute the light within the target area. Here again, these optical units overcome many of the problems associated with LED illumination systems. They nevertheless pose certain other problems relating to bringing the components together in assembly to provide a compact, easy to install and adjust unit suitable for use in a hand-held long range scanner as opposed to a scanner that reads barcodes in contact.
It is, therefore, a primary object of the present invention to improve barcode readers.
A further object of the invention is to improve hand-held barcode scanners for long range illumination and reading of a barcode target.
A still further object of the present invention is to improve optical devices for use in barcode scanners which are capable of producing a sharply defined line of illumination in barcode space using light emitting diodes.
Another object of the present invention is to simplify the assembly of barcode readers using coplanar light emitting diode illumination systems.
Yet another object of the present invention is to provide a single molded frame for holding and positioning the components of a barcode reader.
Yet a further object of the present invention is to more effectively utilize the light emitted by LEDs in a barcode scanner.
These and other objects of the present invention are attained by means of an optical assembly for use in a barcode reader that includes a molded support frame having a rear housing and a pair of arms outwardly extending from the front of the housing. A solid state imager is contained in the housing and an imaging lens is slidably contained between the arms in a rear guideway for focusing an image in barcode space along an optical axis onto the image recording surface of the solid state imager. An aperture card is also slidably contained between the arms in a second front guideway. The aperture card has a vertically disposed stop aperture which is centered about the optical axis of the system. A lamp support unit is mounted on the arms on either side of the imaging lens. Each unit contains a pair of light emitting diodes that are in coplanar alignment with the imaging lens and a horizontally disposed field aperture positioned in front of the light emitting diodes. A single horizontally extended half cylinder optical element is mounted at the distal end of the two arms so that the optical element is centered upon the optical axis of the system with the piano surface facing the imaging lens in perpendicular alignment with the optical axis. An opening is formed in the center of the optical element through which an image of a barcode target can pass optically undisturbed. The outer ends of the optical element form cylindrical lenses for magnifying and focussing the light passing through the two stop apertures in barcode space. A single axis diffuser is positioned at the piano surface of each cylindrical lens which distributes the light from the LEDs horizontally and homogenizes the light across the barcode target area.